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We are working on maltose- and maltotriose-negative yeasts as part of several bachelor theses. In the first case, these yeasts only utilize glucose, fructose and sucrose (some even only glucose and fructose); maltotriose-negative yeasts also utilize maltose, which is the sugar with the highest concentration in the wort in the industrial high-short mashing process, but also in our isothermal high-temperature mashing process. However, maltotriose, the second most common sugar, is not utilized. The difference in alcohol content between beers fermented with maltotriose-positive ("normal") and maltotriose-negative yeasts is usually less than 1 % vol. A wort with an original gravity of around 11.5 °P, which was produced using the high-short mashing process, would have approx. 5% alcohol by volume if fermented with a normal yeast, which therefore utilizes the maltotriose, and approx. 4.3 - 4.4 % alcohol by volume. However,
large breweries rarely use such top-fermenting yeasts, as it is very difficult to prevent normal yeasts from entering the fermentation vessel from the brewery air. At the latest during secondary fermentation, a normal yeast would assert itself and ultimately ferment the maltotriose. A brewery would therefore have to use only such yeasts from the outset, and even then it could not be ruled out that normal yeasts would be introduced from outside. Such a beer would therefore have to be pasteurized very quickly or undergo ultra-fine filtration, which is not easy to implement in everyday industrial brewing. It is even more difficult with maltose-negative yeasts, which almost always require pasteurization.
Secondary results from bachelor theses have shown that alcohol-free beers with less than 0.5 % vol (the current legal limit for alcohol-free) can be produced with the new maltose-negative yeast "LoNa" from Lallemand Brewing (LoNa stands for Low and No alcohol). These have already been drunk at Clausthal University of Technology and received positive reviews because they lack the malt beer character of current commercial alcohol-free beers.
However, we have observed that fermentation is not entirely unproblematic. In two of six experiments, we did indeed obtain a maximum of 0.5% alcohol by volume at around 7 °P. In two other experiments, the alcohol content was stable for several days after completion of the main fermentation, after which a further fermentation began with the final result of 1.8 % vol. at 7 °P. Here, normal yeasts found their way into the wort from the air, and so the maltose and maltotriose were also fermented, even though the fermentation vessels and all equipment and hoses in contact with the wort had been pasteurized or even sterilized beforehand.
In two further experiments, we even achieved alcohol contents of 3.5% vol. at 7 °P. The most likely cause of these beers was that the aroma hops were still enzymatically active during the procedure used, higher unfermentable sugars were converted to fermentable sugars and therefore fermentation continued slowly. We are familiar with this behavior and it is known to us as the "hop creep effect". From these experiments with maltose- and maltotriose-negative yeasts, however, we were also able to derive a safe and sufficiently long time window within which we must pasteurize these beers.
We have already reported on pasteurization here. Specifically, we filled a number of finally fermented young beers into unpressurized kegs and heated them to 65 °C in a sealed water bath for a certain period of time. This reliably kills yeasts and possibly also bacteria, and these beers must then be forcibly carbonated under high-purity conditions (to reliably exclude the introduction of foreign yeasts). We carried out such pasteurization tests in January and we are looking forward to the taste results.
Following these very detailed results from the bachelor theses, we will also focus on the production of various non-alcoholic beers, including wheat beers, in 2024. It should be mentioned at this point that there are maltose-negative yeasts with which it is also possible to produce non-alcoholic beers with 0.0% alcohol by volume under certain demanding conditions. Unless a person has a deficiency in alcohol dehydrogenase, beers with a maximum of 0.5% alcohol by volume are not critical, taking into account the current legal situation. Incidentally, apple juice contains 0.3 - 0.4 % alcohol by volume, a ripe banana can contain 1 % m/m alcohol, and grape juice can contain 1 % alcohol by volume. However, we expect that the EU will tighten these limits in the future and push for lower alcohol content in one way or another.
And now we come to our isothermal high-temperature mashing process. We have reported on this thoroughly new process in numerous articles on this website, and we now know in detail all the conceivable but manageable pitfalls. For original wort between 11 and 12 °P, the lowest value we have ever achieved with normal yeasts is 2.2% alcohol by volume. Our Pilsner brewed on 17.11.2023 has an alcohol content of only 2.5 % vol. at 11 °P, which is about half that of a commercial Pilsner beer.
At the beginning of January, such beers were offered to more than 50 guests at a blind tasting in a hotel in northern Germany, and the guests did not notice the low alcohol content in terms of taste. Around midnight, a guest approached the author of these lines to ask what was wrong with the beers. He had now drunk 6 half pints (0.5 liters each) within 6 hours and didn't notice anything at all. The following scientific explanation surprised but also convinced him. We are therefore certain that we are on the right track with this brewing process.
So on January 24, we brewed another Pilsner. Our new MattMill Professional 120 was used for milling, which not only runs very quietly but, together with a hood to which the malt bags are attached, is characterized by negligible dust generation. The batch consisted of 100% Pale Ale malt and was mashed in parallel in our BrewTower 180+ and in the BrewTools 150 Pro. This was solely due to time constraints, as time is always a bit tight towards the end of the lecture period.
Incidentally, we will only brew front wort beers in future, i.e. the malt is mashed into a quantity of water determined in preliminary tests, followed by an isothermal rest between 72 and 78 °C. After 60 minutes at the latest, lautering starts and we deliberately do not give up any secondary malting. We only need slightly more malt to compensate for the losses caused by not washing out the spent grains to achieve the desired original wort.
For a microbrewery, it is not absolutely necessary to squeeze every last molecule of sugar out of the malt. Not surprisingly, we obtained identical original wort in both systems within the margin of error. We used a new non-isomerized bitter hop extract from Yakimachief for bitter hopping and Alsatian Strisselspalter for whirlpool hopping at around 90 °C. The two wort varieties are fermented together in our "Tank Siegfried" with the WhiteLabs WLP 830 at 12 °C. At approx. 11.5 °P, we expect an alcohol content of 3 % vol.